Grinding apparatus

ABSTRACT

A grinding apparatus includes a table that holds a workpiece, and a grinding unit including a grinding wheel mounted to a spindle. The grinding wheel has a grindstone formed by binding abrasive grains with a bonding agent. In addition, the grinding apparatus further includes: a supply unit that supplies grinding water to at least the grindstone when grinding the workpiece; and a light applying unit that is disposed adjacent to the table and that applies light to a grinding surface of the grindstone grinding the workpiece held by the table. The light applying unit includes a light emission section that emits light, and a diffusion preventive wall that surrounds the light emission section and prevents diffusion of the light.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a grinding apparatus including aholding table that holds a workpiece, and a grinding unit (grindingmeans) having a grinding wheel for grinding the workpiece held by theholding table.

Description of the Related Art

A plate-shaped workpiece such as a semiconductor wafer is ground by agrinding apparatus (see, for example, Japanese Patent Laid-open No.2001-284303) to be thinned to a predetermined thickness, and isthereafter divided by a cutting apparatus or the like into individualdevice chips, which are utilized for various electronic apparatuses andthe like.

SUMMARY OF THE INVENTION

In the case where the wafer is formed of a difficultly grindablematerial such as gallium nitride (GaN), silicon carbide (SiC) or galliumarsenide (GaAs), there is a problem that the wearing amount of agrindstone of a grinding wheel is large and production cost is raisedthereby. In addition, in the case of grinding a wafer formed of a metalor a wafer in which metallic electrodes are partly exposed at a surfaceto be ground of the wafer, there is a problem that ductility of themetal makes it difficult to perform grinding.

It is therefore an object of the present invention to restrain excessivewear of a grindstone and to enable smooth grinding, in the case ofgrinding a wafer formed of a difficultly grindable material or a waferincluding a metal.

In accordance with an aspect of the present invention, there is provideda grinding apparatus including a holding table that holds a workpiece,and a grinding unit including a spindle and a grinding wheel that ismounted to the spindle and that grinds the workpiece held by the holdingtable. The grinding wheel has a grindstone formed by binding abrasivegrains with a bonding agent. The grinding apparatus further includes: agrinding water supply unit that supplies grinding water to at least thegrindstone when the workpiece held by the holding table is ground by thegrinding unit; and a light applying unit that is disposed adjacent tothe holding table and that applies light to a grinding surface of thegrindstone grinding the workpiece held by the holding table. The lightapplying unit includes a light emission section that emits light, and adiffusion preventive wall that surrounds the light emission section andthat prevents diffusion of the light.

Preferably, the light applying unit is disposed on a rotationaltrajectory of the grinding wheel in such a manner as to face thegrinding surface of the grindstone, and the diffusion preventive wall isformed with an entrance section through which the grinding wheel entersand an exit section through which the grinding wheel exits.

Preferably, the grindstone has the abrasive grains and photocatalystgrains bound by the bonding agent, and the light applying unit appliesthe light that excites the photocatalyst grains.

In addition, the bonding agent is preferably a vitrified bond.

In the grinding apparatus according to the present invention, thegrinding wheel has the grindstone formed by binding the abrasive grainswith the bonding agent, the grinding apparatus further includes: thegrinding water supply unit that supplies grinding water to at least thegrindstone when the workpiece held by the holding table is ground by thegrinding unit; and the light applying unit that is disposed adjacent tothe holding table and that applies light to the grinding surface of thegrindstone grinding the workpiece held by the holding table, and thelight applying unit includes the light emission section that emitslight, and the diffusion preventive wall that surrounds the lightemission section and that prevents diffusion of the light. Therefore,during grinding, the light produced by the light emission section isprevented from diffusing by the diffusion preventive wall, whereby theefficiency of application of the light to the grinding surface of thegrindstone is enhanced, and, with the grindstone cutting into theworkpiece being efficiently made hydrophilic or the like, it is possibleto enhance the cooling effect of the grinding water, thereby to restrainwearing of the grindstone, and to enhance a swarf discharging property.Further, with the grindstone made hydrophilic or the like, grindingwater is effectively supplied into the processing region where thegrindstone grinds the workpiece, and, therefore, processing quality canbe prevented from being lowered due to processing heat, and smoothgrinding can be achieved even in the case where the workpiece is a waferformed of a difficultly grindable material.

In addition, where the grindstone is formed by binding the abrasivegrains and the photocatalyst grains with the bonding agent and the lightapplying unit applies light that excites the photocatalyst grains, it isensured that the grinding water supplied exhibits an oxidizing power dueto hydroxyl radicals. Therefore, even if the workpiece is a waferformed, for example, of a difficultly grindable material, it is possibleto oxidize the surface to be ground of the workpiece by the strongoxidizing power of the thus produced hydroxyl radicals, to performgrinding while embrittling the surface through the oxidation, and tosmoothly grind the workpiece. Similarly, even when the workpiece is awafer formed of a metal or a wafer in which metallic electrodes arepartly exposed at the surface to be ground of the wafer, grinding can beperformed while embrittling the metal through oxidation by the strongoxidizing power of hydroxyl radicals, and, therefore, the workpiece canbe ground smoothly.

With the vitrified bond used as the bonding agent in the grindstone, theproperty of making hydrophilic or the like the grindstone by applicationof light thereto can be enhanced more.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view depicting an example of a grindingapparatus;

FIG. 2 is a perspective view depicting an example of a grinding wheel;

FIG. 3 is a front view depicting, in an enlarged form, part of agrindstone;

FIG. 4 is a perspective view depicting an example of positional relationof a grinding unit, a holding table and a light applying unit;

FIG. 5 is an end view depicting a state in which a workpiece held by aholding table is being ground by the grindstone;

FIG. 6A is an illustration, as viewed from above, of positional relationof a rotational trajectory of a grinding wheel, a processing region ofprocessing of the workpiece by the grindstone, and the light applyingunit during grinding;

FIG. 6B is an illustration, as viewed from a lateral side, of a state inwhich the grindstone immediately after application of light to agrinding surface is cutting into the workpiece; and

FIG. 7 is an end view partly depicting a state in which cleaning wateris supplied toward a cover over a light emission section duringgrinding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A grinding apparatus 1 depicted in FIG. 1 is an apparatus that grinds aworkpiece W held on a holding table 30 by a grinding unit (grindingmeans) 7 provided with a grinding wheel 74. A front side (−Y directionside) on a base 10 of the grinding apparatus 1 is a mounting/detachingregion A in which the workpiece W is mounted onto and detached from theholding table 30, and a rear side on the base 10 is a grinding region Bin which grinding of the workpiece W is conducted by the grinding unit7. Input means 12 through which an operator inputs processing conditionsand the like to the grinding apparatus 1 is disposed on the front sideon the base 10.

The holding table 30 is, for example, circular in outer shape, andincludes a suction holding section 300 that holds the workpiece W bysuction, and a frame body 301 that supports the suction holding section300. The suction holding section 300 communicates with a suction source(not depicted), and the workpiece W is suction held on a holding surface300 a which is an exposed surface of the suction holding section 300.The holding surface 300 a of the holding table 30 is formed in the shapeof a conical surface having an extremely gentle inclination with arotational center of the holding table 30 as a peak. The holding table30 is surrounded by a cover 31 from the surroundings, is rotatable aboutan axis set in the vertical direction, and can be reciprocated in aY-axis direction between the mounting/detaching region A and thegrinding region B by Y-axis direction feeding means (not depicted)disposed on the lower side of the cover 31 and a bellows cover 31 aconnected to the cover 31.

A column 11 is erectly provided in the grinding region B, and grindingfeeding means 5 for putting the grinding unit 7 into grinding feeding ina Z-axis direction is disposed on a lateral side of the column 11. Thegrinding feeding means 5 includes a ball screw 50 having an axis in theZ-axis direction, a pair of guide rails 51 disposed in parallel to theball screw 50, a motor 52 that is connected to an upper end of the ballscrew 50 and rotates the ball screw 50, a lift plate 53 a nut in theinside of which is in screw engagement with the ball screw 50 and sideportions of which make sliding contact with the guide rails 51, and aholder 54 that is connected to the lift plate 53 and holds the grindingunit 7. When the motor 52 rotates the ball screw 50, the lift plate 53is reciprocated in the Z-axis direction while guided by the guide rails51 attendant on this, and the grinding unit 7 held by the holder 54 isput into grinding feeding in the Z-axis direction.

The grinding unit 7 includes a spindle 70 having an axial direction inthe Z-axis direction, a housing 71 that supports the spindle 70 in arotatable manner, a motor 72 that rotationally drives the spindle 70, amount 73 connected to a tip of the spindle 70, and a grinding wheel 74detachably mounted to a lower surface of the mount 73.

The grinding wheel 74 depicted in FIG. 2 includes an annular wheel base74 b, and a plurality of substantially rectangular parallelepipedgrindstones 74 a arranged in an annular pattern on a bottom surface(free end portion) of the wheel base 74 b. An upper surface of the wheelbase 74 b is provided with tapped holes 74 c, and jet ports 74 d throughwhich grinding water is jetted toward the grindstones 74 a. As depictedin FIG. 3, the grindstone 74 a in the present embodiment is formed bymixing diamond abrasive grains P1 with photocatalyst grains P2 such astitanium oxide (TiO₂) grains, and binding the mixture by a vitrifiedbond B1, which is a vitrified or ceramic bonding agent. The grindingwheel 74 is mounted to a lower surface of the mount 73 by putting screws73 a depicted in FIG. 1 into screw engagement with the tapped holes 74 cin the wheel base 74 b through holes provided in the mount 73.

The shape of the grindstone 74 a may be an integral annular shape, andthe photocatalyst grains P2 may be tin oxide grains, zinc oxide grains,cerium oxide grains or the like. Note that the grindstone 74 a may notcontain the photocatalyst grains P2, and a bonding agent other than thevitrified bond may be used as the bonding agent therein.

A method of manufacturing the grinding wheel 74 is as follows. First,the vitrified bond B1 is mixed with diamond abrasive grains P1 of #1000in grain size, and the resultant mixture is further mixed with thephotocatalyst grains P2, followed by stirring. As the vitrified bond B1,for example, silicon dioxide (SiO₂) is used as a main constituent, whichmay be admixed with a trace amount of additive for controlling themelting point. Next, this mixture is heated at a predeterminedtemperature, followed further by pressing to mold the mixture into asubstantially rectangular parallelepiped shape. Thereafter, sintering isfurther conducted at a high temperature for several hours, to produce agrindstone 74 a. The content of the photocatalyst grains P2 in thegrindstone 74 a is 15 wt %, for example. A plurality of the grindstones74 a thus produced are arranged in an annular pattern and fixed to abottom surface of the wheel base 74 b, to manufacture the grinding wheel74. Note that the grain size of the diamond abrasive grains P1 is notlimited to the example in the present embodiment, and may beappropriately modified according to the kind and content of thephotocatalyst grains P2 and the like factors.

In the inside of the spindle 70 depicted in FIG. 1, a channel 70 a whichcommunicates with a grinding water supply unit (grinding water supplymeans) 8 for supplying grinding water to the grindstones 74 a and whichserves as a passage of the grinding water is provided penetrating in theaxial direction (Z-axis direction) of the spindle 70, such that thegrinding water having passed through the channel 70 a can pass throughthe mount 73 and be jetted from the wheel base 74 b toward thegrindstones 74 a.

The grinding water supply unit 8 includes a grinding water source 80reserving water (for example, pure water), a piping 81 connected to thegrinding water source 80 and communicating with the channel 70 a, and acontrol valve 82 disposed at an arbitrary position on the piping 81 forcontrolling the quantity of the grinding water supplied, and suppliesthe grinding water to the grindstones 74 a at least.

As illustrated in FIGS. 1 and 4, the grinding apparatus 1 includes alight applying unit (light applying means) 9 that is disposed adjacentto the holding table 30 and that applies light to grinding surfaces(lower surfaces) of the grindstones 74 a grinding the workpiece W heldby the holding table 30. As depicted in FIG. 4, the light applying unit9 includes, for example, a base section 90 having a substantiallyarcuate outer shape, a plurality of (in the example illustrated, four)light emission sections 91 alignedly disposed on an upper surface of thebase section 90, a cleaning water supply section 92 that suppliescleaning water (for example, pure water) toward the light emissionsections 91, a cover 93 that prevents dirt from adhering to the lightemission sections 91, and a diffusion preventive wall 94 that surroundsthe light emission sections 91 and prevents diffusion of the light.

For example, the light emission sections 91 embedded in dents formed inthe upper surface of the base section 90 are of light emitting diode(LED) illumination that can emit light of a predetermined wavelength,and can be switched between an ON state and an OFF state by a powersource (not depicted). Note that in the case where the photocatalystgrains P2 contained in the grindstones 74 a are titanium oxide grains asin the present embodiment, the wavelength of the light (ultraviolet (UV)light) produced by the light emission sections 91 is, for example,preferably 201 nm to 400 nm, and more preferably 201 nm to 365 nm.

Note that in the case where the grindstone 74 a does not contain thephotocatalyst grains P2, the light emission section 91 is preferably alow pressure mercury lamp or a two-wavelength LED that can emit light attwo wavelengths, and is preferably able to emit light of a wavelength of80 nm to 200 nm (for example, a wavelength of 185 nm) and light of awavelength of 240 nm to 280 nm (for example, a wavelength of 254 nm). Itis natural that in the case where the grindstone 74 a does not containthe photocatalyst grains P2, light of a wavelength of 201 nm to 365 nmmay be applied thereto.

The plate-shaped cover 93 is composed, for example, of a transparentmember such as a glass, and is fixed on the upper surface of the basesection 90 in such a manner as to cover the light emission sections 91.For example, the base section 90 is movable in the vertical direction,such that when performing grinding, the height position of an uppersurface of the cover 93 can be set to a desired height position takinginto account a grinding feeding position of the grindstones 74 a.

The cleaning water supply section 92 includes, for example, a cleaningwater source (not depicted) in which water is reserved, and a cleaningwater nozzle 920 communicating with the cleaning water source. Thecleaning water nozzle 920 is, for example, fixed to a side surface ofthe base section 90 in such a manner as to lie along the base section90, and a plurality of narrow width slit-formed jet ports 920 a forjetting cleaning water toward the cover 93 covering the light emissionsections 91 are aligned in the longitudinal direction of the cleaningwater nozzle 920. The jet ports 920 a has a shape, a size, an anglerelative to the light emission section 91, etc. set in such a mannerthat the flow of the cleaning water jetted can be straightened on theupper surface of the cover 93.

The diffusion preventive wall 94 surrounding the light emission sections91 includes, for example, an outer plate 940 and an inner plate 941. Theouter plate 940 and the inner plate 941 are formed by curving a metallicplate of SUS or the like following the outer shape of the base section90, and are fixed individually to side surfaces of the base section 90.The outer plate 940 and the inner plate 941 are formed with drain ports(not depicted), and cleaning water having been jetted from the cleaningnozzle 920 and having cleaned the upper surface of the cover 93 flowsdown from the upper surface of the cover 93 and is then dischargedthrough the drain ports to the outside of the diffusion preventive wall94. The diffusion preventive wall 94 is formed with an entrance section94 a through which the grinding wheel 74 enters and an exit section 94 bthrough which the grinding wheel 74 exits. The entrance section 94 a andthe exit section 94 b are formed in such a size that at least thegrindstones 74 a can pass therethrough. In FIG. 4, inside surfaces ofthe outer plate 940 and the inner plate 941 are smooth curved surfaces,but this is not restrictive; the outer plate 940 and the inner plate 941may be formed by bending at a predetermined angle and their insidesurfaces may be in the form of a polyhedron.

An operation of the grinding apparatus 1 depicted in FIG. 1 in the caseof grinding the workpiece W by use of the grinding apparatus 1 will nowbe described below.

The circular disk-shaped workpiece W depicted in FIG. 1 is, for example,a semiconductor wafer formed of SiC which is difficult to grind, amultiplicity of devices are formed in regions partitioned in a gridpattern by streets (division lines) on a front surface Wa of theworkpiece W directed to the lower side in FIG. 1, and a protective tapeT for protecting the front surface Wa is adhered thereto. A back surfaceWb of the workpiece W is a surface to be ground by the grinding wheel74. Note that the shape and kind of the workpiece W are not particularlylimited, but can be appropriately modified in relation to the grindingwheel 74; examples of the applicable workpiece W include a wafer formedof GaAs, GaN or the like, a wafer formed of a metal, and a wafer inwhich metallic electrodes are partly exposed to the back surface side ofthe wafer.

First, in the mounting/detaching region A, the workpiece W is placed onthe holding surface 300 a of the holding table 30, with its back surfaceWb on the upper side. Then, a suction force generated from a suctionsource (not depicted) is transmitted to the holding surface 300 a,whereby the holding table 30 holds the workpiece W on the holdingsurface 300 a by suction. The workpiece W is in the state of beingsuction held along the holding surface 300 a which is a gently inclinedconical surface.

The holding table 30 is moved in a +Y direction to a position under thegrinding unit 7 by the Y-axis direction feeding means (not depicted),whereby aligning of the grinding wheel 74 and the workpiece W held bythe holding table 30 is performed. The aligning is conducted, forexample, in such a manner that the rotational center of the grindingwheel 74 is deviated by a predetermined distance in the +Y directionfrom the rotational center of the workpiece W, and the rotationaltrajectory of the grindstones 74 a passes the rotational center of theworkpiece W. In addition, the inclination of the holding table 30 isadjusted such that the holding surface 300 a which is a gently inclinedconical surface becomes parallel to the grinding surfaces which arelower surfaces of the grindstones 74 a, whereby the back surface Wb ofthe workpiece W is made to be parallel to the grinding surfaces of thegrindstones 74 a.

After the aligning of the grinding wheel 74 and the workpiece W isperformed, the spindle 70 is rotationally driven by the motor 72, and,attendant on this, the grinding wheel 74 is rotated counterclockwise asviewed from the +Z direction side, as depicted in FIG. 5. In addition,the grinding unit 7 is fed in the −Z direction by the grinding feedingmeans 5, and the grinding wheel 74 is gradually lowered in the −Zdirection, and the grindstones 74 a come into contact with the backsurface Wb of the workpiece W, whereby grinding is performed. Further,during the grinding, the workpiece W is also rotated attendant on therotation of the holding table 30 in the counterclockwise direction asviewed from the +Z direction side, so that the grindstones 74 a performgrinding of the whole area of the back surface Wb of the workpiece W.

During the grinding, the grinding water supply unit 8 supplies grindingwater into the channel 70 a in the spindle 70. As depicted in FIG. 5,the grinding water supplied into the channel 70 a passes throughchannels 73 b formed inside the mount 73 at regular intervals in thecircumferential direction of the mount 73, and, further, is jettedthrough the jet ports 74 d of the wheel base 74 b toward the grindstones74 a.

Since the workpiece W is suction held on the holding surface 300 a,which is a gently inclined conical surface, of the holding table 30along the holding surface 300 a, the grindstones 74 a make contact with,and grind, the workpiece W in a region E (hereinafter referred to asprocessing region E) in the rotational trajectory e of the grindingwheel 74 indicated by alternate long and two short dash lines in FIG.6A.

For example, in a state in which the aligning of the grinding wheel 74and the holding table 30 has been conducted, the light applying unit 9disposed adjacent to the holding table 30 is disposed on the immediatelyupstream side of a position at which the grindstones 74 a enter theprocessing region E, as depicted in FIG. 6A. In addition, as depicted inFIG. 6B, the light applying unit 9 is disposed on the rotationaltrajectory e of the grinding wheel 74 in such a manner as to face thegrinding surfaces (lower surfaces) of the grindstones 74 a. Attendant onthe start of grinding, the light emission sections 91 are put into an ONstate, and the light emission sections 91 emit light (UV light) of awavelength of approximately 365 nm, for example. Then, when thegrindstones 74 a of the grinding wheel 74 being rotated enter the insideof the diffusion preventive wall 94 via the entrance section 94 a, thelight produced by the light emission sections 91 is transmitted throughthe cover 93, to be applied to the grinding surfaces of the grindstones74 a in the inside of the diffusion preventive wall 94. Since thediffusion preventive wall 94 prevents the light produced by the lightemission sections 91 from diffusing and the light is collected onto thegrinding surfaces of the grindstones 74 a passed on the upper side inthe inside of the diffusion preventive wall 94, the efficiency ofapplication of the light to the grinding surfaces of the grindstone 74 ais improved as compared to that in the related art.

By the application of the light, the photocatalyst grains P2 mixedlypresent in the grindstones 74 a are excited, that is, electrons in avalence band of the photocatalyst grains P2 are excited, whereby twokinds of carriers, namely, electrons and holes, are generated. The holesgenerated in the photocatalyst grains P2 mixedly present in thegrindstones 74 a oxidize the grinding water coming into contact with thesurfaces of the photocatalyst grains P2, thereby producing hydroxylradicals having a high oxidizing power. Therefore, the grinding waterhaving contacted the grinding surfaces of the grindstones 74 a exitingthrough the exit section 94 b is given the oxidizing power due to thehydroxyl radicals on at least the back surface Wb of the workpiece W.

Since the workpiece W formed of SiC is embrittled through oxidation bythe hydroxyl radicals thus produced, it becomes easy to grind theworkpiece W by the grinding wheel 74. In addition, the time of presenceof the hydroxyl radicals thus produced is very short, and, therefore,other oxidation than that of the back surface Wb of the workpiece W bythe grinding water is not generated. In addition, the jetted grindingwater functions also to cool the part of contact between the grindstones74 a and the back surface Wb of the workpiece W and to remove grindingswarf generated at the back surface Wb of the workpiece W.

Note that even where, for example, the workpiece W is a wafer formed ofa metal or a wafer in which metallic electrodes are partly exposed tothe back surface side of the wafer, grinding can be performed whileembrittling the metal through oxidation by the strong oxidizing power ofthe hydroxyl radicals, so that smooth grinding of the workpiece can beachieved.

In addition, the grinding surfaces of the grindstones 74 a formed usingthe vitrified bond B1 as a bonding agent are enhanced in hydrophilicitythrough, for example, formation of highly polar hydrophilic groups byapplication of light, so that the grinding water becomes less liable toform droplets on the grinding surfaces of the grindstones 74 a, and thegrinding water becomes liable to spread in a water film form over thewhole grinding surfaces of the grindstones 74 a. Therefore, thegrindstones 74 a thus made hydrophilic enter the processing region Ewhile being accompanied by much grinding water, and grind the backsurface Wb of the workpiece W. With more grinding water entering thearea of contact between the back surface Wb of the workpiece W and thegrinding surfaces of the grindstones 74 a, generation of frictional heatin the area of contact is restrained. Consequently, excessive wear ofthe grindstones 74 a can be restrained, and a swarf discharging propertycan be enhanced. Further, with the grindstones 74 a made hydrophilic,the grinding water is effectively supplied into the processing region Ewhere the grindstones 74 a grind the workpiece W, and, accordingly,processing quality can be prevented from being lowered due to processingheat.

Note that in the case where the grindstone 74 a does not contain thephotocatalyst grains P2, the light emission sections 91 may apply, forexample, UV light of a wavelength of 185 nm and UV light of a wavelengthof 254 nm toward the grindstones 74 a. With the UV light of thewavelength of 185 nm applied to the grinding surfaces of the grindstones74 a, oxygen molecules in air present between the lower surfaces of thegrindstones 74 a and the light emission sections 91 absorb the UV light,whereby oxygen atoms in a ground state are produced. The oxygen atomsthus produced combine with oxygen molecules in the surroundings, toproduce ozone. Further, ozone thus produced absorbs the UV light of thewavelength of 254 nm, whereby active oxygen in an excited state isproduced. Since active oxygen and ozone have a high oxidizing power,they combine with carbon, hydrogen or the like generated at the grindingsurfaces of the grindstones 74 a, to produce highly polar hydrophilicgroups on the grinding surfaces of the grindstones 74 a, resulting inthat the grindstones 74 a are made to be hydrophilic.

In addition, as depicted in FIG. 7, during grinding, the cleaning watersupply section 92 supplies cleaning water to the cover 93 over the lightemission sections 91. Specifically, the cleaning water jetted from thecleaning water nozzle 920 onto the cover 93, whose flow is appropriatelystraightened, remove dirt such as grinding swarf deposited on the cover93, whereby the light generated by the light emission sections 91 duringgrinding can always be appropriately applied to the processing surfacesof the grindstones 74 a. The cleaning water having flowed down from theupper surface of the cover 93 is discharged through the drain ports (notdepicted) to the outside of the diffusion preventive wall 94.

According to an example of experimental results obtained with respect togrinding, grinding of a workpiece W formed of SiC by 50 μm by use of aconventional grinding apparatus took 110 seconds, whereas the grindingby use of the grinding apparatus 1 according to the present inventiontook only 90 seconds, so that a shortening of grinding time could berealized. In addition, in grinding of a Si surface of a workpiece W, 83%of the whole part of the grindstones of a conventional grindingapparatus was worn where the grinding amount was 100, whereas the wearof the grindstones 74 a of the grinding apparatus 1 according to thepresent invention was only 57% of the whole part where the grindingamount was 100. Further, in grinding of a C surface of a workpiece W,60% of the whole part of the grindstones of a conventional grindingapparatus was worn where the grinding amount was 100, whereas the wearof the grindstones 74 a of the grinding apparatus 1 according to thepresent invention was only 39% of the whole part where the grindingamount was 100.

The present invention is not limited to the details of the abovedescribed preferred embodiment. The scope of the invention is defined bythe appended claims and all changes and modifications as fall within theequivalence of the scope of the claims are therefore to be embraced bythe invention.

What is claimed is:
 1. A grinding apparatus comprising: a holding tablethat holds a workpiece; and a grinding unit including a spindle and agrinding wheel that is mounted to the spindle and that grinds theworkpiece held by the holding table, wherein the grinding wheel has agrindstone formed by binding abrasive grains with a bonding agent, andthe grinding apparatus further comprises: a grinding water supply unitthat supplies grinding water to at least the grindstone when theworkpiece held by the holding table is ground by the grinding unit; anda light applying unit that is disposed adjacent to the holding table andthat applies light to a grinding surface of the grindstone grinding theworkpiece held by the holding table, and the light applying unitincludes a light emission section that emits light, a diffusionpreventive wall that surrounds the light emission section and thatprevents diffusion of the light and a cleaning water supply section forsupplying cleaning water to remove dirt in the light applying unit. 2.The grinding apparatus according to claim 1, wherein the light applyingunit is disposed on a rotational trajectory of the grinding wheel insuch a manner as to face the grinding surface of the grindstone, and thediffusion preventive wall is formed with an entrance section throughwhich the grinding wheel enters and an exit section through which thegrinding wheel exits.
 3. The grinding apparatus according to claim 1,wherein the grindstone has the abrasive grains and photocatalyst grainsbound by the bonding agent, and the light applying unit applies thelight that excites the photocatalyst grains.
 4. The grinding apparatusaccording to claim 2, wherein the grindstone has the abrasive grains andphotocatalyst grains bound by the bonding agent, and the light applyingunit applies the light that excites the photocatalyst grains.
 5. Thegrinding apparatus according to claim 1, wherein the bonding agent is avitrified bond.
 6. The grinding apparatus according to claim 2, whereinthe bonding agent is a vitrified bond.
 7. The grinding apparatusaccording to claim 3, wherein the bonding agent is a vitrified bond. 8.The grinding apparatus according to claim 4, wherein the bonding agentis a vitrified bond.
 9. The grinding apparatus according to claim 1,wherein the light applying unit further includes a cover provided overthe light emission section, and the cleaning water supply section jetscleaning water onto the cover to remove dirt formed on the cover. 10.The grinding apparatus according to claim 1, wherein the light applyingunit is disposed on an immediately upstream side of a position at whichthe grindstones make contact with the workpiece.